Quantum MIIM Diodes Beat Silicon

PORTLAND, Ore. — Operating at terahertz frequencies much higher than silicon devices while consuming less power and producing less heat, metal-insulator-metal (MIM) diodes are one of those promising technologies always just out of reach.

MIM diodes use quantum tunneling, which permits electrons to jump from one metal electrode to the other without interacting with the intervening insulator layer -- hence the power and heat reductions. So far, their development has been slow going.

Now Oregon State University (OSU) researchers claim to have invigorated the technology by adding a second insulator layer to produce an MIIM device that aims to solve the problems with MIM devices and come closer to taking the technology mainstream.

"What people have typically done is use two different metals on the top and bottom electrodes, but you are limited by the work function difference you can get between the different metals," said OSU professor John Conley in an interview with EE Times. "But by using two different insulators -- one with a large bandgap and one with a smaller bandgap -- we can get extra asymmetry that can even overshadow the asymmetry of the different metals."

The two insulator layers -- which for Conley's work was hafnium oxide and aluminum oxide -- enables what he called "step tunneling." Step tunneling allows more precise control of the diode asymmetry and thus its rectification capabilities at low voltages.

As a result, Conley sees his MIIM devices are poised to improve all sorts of electronic devices in wide use today, from liquid crystal displays to cell phones and televisions, as well as new types of devices such as infrared solar cells that convert radiant heat into electricity.

"The holy grails is an infrared antenna, which would harvest infrared energy in a special infrared solar cell," said Conley.

Next, the researchers hope to optimize their process, then tackle applications that use even more metal-insulator layers, such as transistors.

"This is a building block device -- the MIIM structure by itself is just a diode -- but we plan to put these devices in other structures to improve their performance, such as the MIMIM hot-electron transistor invented by Carver Mead back in the 1960s," said Conley.

Doctoral candidate Nasir Alimardani also contributed to the work, which was funded by the National Science Foundation (NSF), the US Army Research Laboratory, and the Oregon Nanoscience and Microtechnologies Institute.

It definitely IS a tunnel diode. But not a semiconductor but a metal electrode one. The difference is, that the semiconductor tunnel diode of the 60ies shows a region of negative differential resistance which allows some interesting applications as oscillator nd so on. The MIM diode can not show this kind of behavior due to the different band structure of the electrodes.

My current understanding of the MIIM diode is, that its main application is as a demodulator/detecter for very high freqiencies.

A tunneling-based device may be ideally designed or optimized for high nonlinearity. But it should be recognized that tunneling is not expected to be a high current output mechanism matching CMOS. A MOSFET that is off is already a tunneling barrier (reverse bias pn junction depletion zone) with nonlinearity.

Yes quite true, the industries are desperately looking for the CMOS alternative that can work beyond Gigahertz, since this metal alternatives have got bandwidth ranging upto Terahertz, if this time the technology gets commercially accepted it will really open a new era.

Is this about CMOS or the material? I think we can still have CMOS design paradigm with another material beside Silicon. I hope we crack this code soon as it is long overdue. Something needs to help provide a new path for the continuation of Moore's law

Phononscattering "How is this supposed to "beat CMOS" or lead to transistors? My understanding so far is, that this is a two- not three terminal device. So it can not replace a transistor."

For a two terminal device structure, think of light or microwave input as the third terminal. Where the device is mounted in a lightwaveguide or a microwave guide. As we push frequencies higher those two will tend to merge. Quantum coupling efficiency will be the equivalent of gain.

The reliability of MIMs has been a problem in the past and limited widespread use. Given reliability they may find application in optical detectors in high speed backplanes. Who knows when TSVs run out of signal carrying capacity optical detection MIMs might allow TSV to be just holes!!

Ok, after some web searching I found comprehensive information. Seems like the technology itself is not new and has already performed well in the past, but failed commercially due to lack of differentiating applications.